The invention relates to a method and a device according to the preamble of the independent claims where at least one parameter of a mixture is to be determined, the components of which mixture comprise a carrier substance, water and gas.
A method of this type can in particular be used for determining the humidity state of concrete elements. The knowledge of the humidity state of concrete elements is often indispensable for avoiding or assessing of damages, but also for carrying out building and renovation steps. Furthermore, the humidity situation has to be known when laying floors (tiles, parquets, etc) in lofts, when coating concrete surfaces, and when assessing the corrosion of rebars. Hence, the measurement of humidity is of particular importance in concrete construction as well.
Methods of this type can, however, also be used in other fields, such as in the characterisation of pharmaceuticals and food stuff, and wherever a parameter of a mixture of carrier substance, water and gas has to be determined, wherein the carrier substance can be solid or liquid.
In order to keep expense and costs small, a corresponding method should be non-destructive.
A method and a device for determining the humidity content of porous building materials have been known from the patent DE 196 52 679 C1. There, the humidity of the mixture is determined by feeding electromagnetic waves of several frequencies to a sensor and by determining the frequency dependent permittivity value of the mixture by means of calibration data specifically provided for the sensor. By means of a system of equations, based on the mixing formula of Polder-van Santen/de Loor, which is solved for the frequency independent parameters, the volume fraction of the liquid water can be determined.
It has been found, however, that the accuracy of this method is limited.